Elementary astronomy; a beginner's text-book (1899)
Holden, Edward Singleton, 1846-1914 · New York, H. Holt and company · leaf 309
might seem to be whatwe call a purely accidental circumstance, like the occur-rence of cloudy and clear years on the Earth, observationsof sun-spots establish the fact that this number variesperiodically. 288 ASTRONOMY. That the solar spots vary periodically will appear from the follow-ing summary… … Fig. 168.—Appearance of the Same Solar Spot near theCentre of the Sun and near the Edge., Every eleven years there is a minimum number of spots, and aboutfive years after each minimum there is a maximum. There was amaximum of spots in 1893 ; the minimum occurred in 1899. If, in-stead of merely…
Astronomy
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